1. Field of the Invention
The present invention relates to a magneto-optical recording disk onto which information is written or deleted using a rising temperature due to irradiation of laser light and from which a recorded signal is read using a magneto-optical effect. The present invention also relates to a method and device for reproducing information recorded on the magneto-optical recording disk.
2. Description of the Related Art
In magneto-optical recording, a portion of a magnetic film of a magneto-optical recording medium is locally heated to a Curie point or compensation composition temperature or higher by irradiation of laser light. The heated portion is magnetized in the direction of an external magnetic field, thereby forming a recording magnetic domain where an information signal is recorded. The magnetic film onto which the information signal is recorded is also referred to as a recording magnetic film (or simply recording film).
Among such magneto-optical recording methods for the magneto-optical recording medium is a magnetic field modulation recording method. In this method, the temperature of an overall recording magnetic film is increased by irradiation of laser light. An external magnetic field having a modulated direction in accordance with a recording signal is applied to a given portion of the recording magnetic film. The recording signal is thermomagnetically recorded on the given portion. This is called a magnetic field modulation recording method. Alternatively, laser light having a modulated intensity in accordance with a recording signal is irradiated onto a given portion of a recording magnetic film. The temperature of the given portion is increased so that the recording signal is thermomagnetically recorded onto the given portion. This is called an optical modulation recording method.
In a conventional magneto-optical recording medium, when the size of the recording magnetic domain is smaller than or equal to the diameter of a reproducing light spot, recording magnetic domains at the front and rear side of the recording magnetic domain which is a target to be reproduced are included in the reproducing light spot (i.e., a detection range). Interference of the adjacent recording magnetic domains causes a decrease in the reproduced signal, whereby the S/N ratio is reduced or the reproduction signal is not output.
A magneto-optical recording and reproducing method using magnetic super-resolution as shown in FIGS. 1A and 1B is a proposed technique to solve such a problem (see Nikkei Electronics, No. 539, Oct. 28, 1991). This magneto-optical recording and reproducing method will be briefly described below.
As shown in a cross-sectional view of FIG. 1B, a magneto-optical recording medium 60 includes a reproducing magnetic film 63, a transcribing magnetic film 64A, an intermediate film 64, and a recording magnetic film 65 which are successively provided on a substrate (not shown). An arrow X in FIG. 1B indicates a moving direction along a track of the magneto-optical recording medium 60. An upward arrow 61 indicates a magnetic field for recording and reproduction. A downward arrow 62 indicates an initial magnetic field.
FIG. 1A is a plan view illustrating a part of a track of the magneto-optical recording medium 60.
As shown in FIGS. 1A and 1B, when reproducing information, a reproducing light spot 67 is formed along the track. When laser light is irradiated onto the rotating magneto-optical recording medium 60, the temperature distribution of a magnetic film structure including the reproducing magnetic film 63 and the transcribing magnetic film 64A are not rotation symmetrical around the center of the circular reproducing light spot 67. Specifically, a region 70 which has been irradiated by the reproducing light spot 67 has a high temperature greater than or equal to the Curie temperature Tc of the transcribing magnetic film 64A (the region 70 is referred to as a high temperature region 70). A crescent-shaped region 72, which is positioned at the left side of the reproducing light spot 67 and outside the high temperature region 70, has an intermediate temperature (the region 72 is referred to as an intermediate temperature region 72). A region 71 which is positioned at the right side of the intermediate temperature region 72 and within the reproducing light spot 67 has a low temperature (the region 71 is referred to as a low temperature region 71).
Assuming that a signal (information) is already thermomagnetically recorded as a recording magnetic domain 69 on the recording magnetic film 65, the transcribing magnetic film 64A is strongly exchange-coupled with the reproducing magnetic film 63. The intermediate film 64 is provided in such a manner that the magnetic domain wall becomes stable when the magnetization direction of the reproducing magnetic film 63 is in agreement with the magnetization direction of the recording magnetic film 65.
The reproducing operation of the magneto-optical recording medium 60 thus constructed will be described below.
The reproducing magnetic film 63 initially has the same magnetization direction as that of the initializing magnetic field 62. Upon reproduction, laser light for reproduction is irradiated to a range between X1 and X2 shown in FIG. 1B. The laser light forms the reproducing light spot 67 on the rotating magneto-optical recording medium 60. This causes an increase in temperature of the rotating magneto-optical recording medium 60, resulting in a temperature distribution shown in FIG. 1A (i.e., the temperature region 70, 71, and 72). The coercive force of the reproducing magnetic film 63 is decreased due to the temperature increase. Exchange-coupling with the recording magnetic film 65 is therefore dominant in the intermediate temperature region 72, so that the magnetization of the reproducing magnetic film 63 is directed to the magnetization direction of the recording magnetic film 65.
In the high temperature region 70 having a temperature of Tc or higher, the magnetization of the transcribing magnetic film 64A disappears in some portions thereof. Exchange-coupling between the reproducing magnetic film 63 and the recording magnetic film 65 is cut off at these portions, so that the magnetization of the reproducing magnetic film 63 is directed to the magnetization direction of the reproducing magnetic field 61. Accordingly, the low and high temperature regions 71 and 70 within the reproducing light spot 67 masks the recording magnetic domains 69. Only from a recording magnetic domain 69X positioned in the intermediate temperature region 72 is information read as a reproduced signal.
With the above-described method, even when a single recording magnetic domain 69 has a size smaller than the diameter of the reproducing light spot 67, there occurs substantially no interference by recording magnetic domains 69 ahead of and behind the single recording magnetic domain 69. It is therefore possible to reproduce information stored in high density.
There is, however, a drawback with the above-described magneto-optical recording medium 60 as it needs the initializing magnetic field 62 for initially directing the magnetization of the reproducing magnetic film 63 in a single direction.
Japanese Laid-Open Publication No. 5-81717 proposes a magneto-optical recording medium 80 having a structure shown in FIGS. 2A and 2B which does not need the initializing magnetic field.
As shown in a cross-sectional view of FIG. 2B, the magneto-optical recording medium 80 includes a reproducing magnetic film 83 and a recording magnetic film 85 on a substrate (not shown). An arrow X represents a moving direction along a track of the magneto-optical recording medium 80. As is different from the magneto-optical recording medium 60 shown in FIGS. 1A and 1B, an in-plane magnetization film is used as the reproducing magnetic film 83 in the magneto-optical recording medium 80.
FIG. 2A is a plan view illustrating part of the track of the magneto-optical recording medium 80. Similar to the magneto-optical recording medium 60 described with reference to FIGS. 1A and 1B, laser light is irradiated in a range between X1 and X2 along the track of FIG. 2B upon reproduction. The laser light forms a reproducing light spot 87. When laser light is irradiated onto the rotating magneto-optical recording medium 80, the temperature distributions of a reproducing magnetic film 83 and a transcribing magnetic film 85 are not rotation symmetrical around the center of the circular reproducing light spot 87. Specifically, a region which has been irradiated by the reproducing light spot 87 and is currently irradiated by a left-end portion of the reproducing light spot 87 forms a high temperature region 90. A region which is included in the reproducing light spot 87 and outside the high temperature region 90 forms a low temperature region 91. Also in this case, a recording magnetic domain 89 is smaller than the reproducing light spot 87.
The reproducing operation of the magneto-optical recording medium 80 thus constructed will be described below.
Assuming that a recording signal has been previously recorded in the recording magnetic domains 89 of the recording magnetic film 85 by the thermomagnetically recording, the reproducing magnetic film 83 is an in-plane magnetization film having a magnetic anisotropy in an in-plane direction parallel to the film at room temperature. Only the high temperature region 90 within the reproducing light spot 87 of the reproducing magnetic film 83 is a vertical magnetization film having a magnetic anisotropy in a direction perpendicular to the film. When laser light for reproduction is irradiated onto a range between X1 and X2 shown in FIG. 2B, the temperature of the magneto-optical recording medium 80 is increased so that the high temperature region 90 and the low temperature region 91 are formed. In the high temperature region 90, the reproducing magnetic film 83 is changed to the vertical magnetization film, and is exchange-coupled with the recording magnetic film 85 so that the magnetization of the reproducing magnetic film 83 is directed to the magnetization direction of the recording magnetic film 85. When the magneto-optical recording medium 80 is moved in the X direction so that the temperature of the magneto-optical recording medium 80 is decreased, the reproducing magnetic film 83 is changed to an in-plane magnetization film.
In the magneto-optical recording medium 80, information stored in the recording magnetic domains 89 which are smaller than the reproducing light spot 87 can thus be reproduced without the initializing magnetic field.
In the magneto-optical recording medium 80, when the reproducing magnetic film 83 includes an in-plane magnetization film, the initialized magnetization field is not necessary. However, there are the following drawbacks.
The magnetization direction of the reproducing magnetic film 83 is attracted toward the recording magnetic film 85 due to magnetic coupling between the reproducing magnetic film 83 and the recording magnetic film 85. For this reason, the magnetization direction of the reproducing magnetic film 83 is not held in an ideal in-plane magnetization direction but has a vertical component of magnetization in the low temperature region 91 even within the light spot. As a result, transcription occurs even in a region which does not need transcription of the recording magnetic domain 89. This leads to insufficient resolution upon reproduction or occurrence of noise upon transcription.
Further, the critical temperature of the reproducing magnetic 83 at which it changes from an in-plane magnetization film to a vertical magnetization film is constant. For this reason, as the reproducing power of a laser beam for reproduction is changed, the region where the recording magnetic domain 89 is transcribed is changed, whereby waveform interference degrades the reproduction characteristic.
Furthermore, as a magneto-optical recording medium having a high resolution and a high-performance reproduction characteristic without the need for an initializing magnetic field, there is a magneto-optical recording medium having a reproducing magnetic film of a shrink type (magnetic domain wall shrink type). Assuming that a recording signal is read only from a particular temperature region within the reproducing light spot, the use of this shrink type reproducing magnetic film leads to an unstable shrink operation in the arrangement including only the recording magnetic film and the reproducing magnetic film. To address this, the decreased magnetic coupling force may allow stabilization of the shrink operation. In this case, there is a problem in that the signal transcription from the recording magnetic film is insufficient.
Furthermore, assuming that the magnetic domain is enlarged by utilizing the shrink operation or magnetic domain wall shift, when a conventional guide groove is used in association with a tracking servo, operation by the magnetic domain wall shift is prevented due to the influence of the guide groove, thereby reducing the amplitude of a reproduced signal. Alternatively, the influence of noise due to the groove causes a reduction in CNR upon reproduction of a signal. The above are also drawbacks.
According to one aspect of the present invention, a magneto-optical recording medium, includes a substrate; and a reproducing layer and a recording layer provided on the substrate. A recording magnetic domain is provided in the recording layer by heating the recording layer by irradiation with light and applying a recording magnetic field to the recording layer in such a manner that information is recorded in the recording layer. The recording layer is a magnetic film having magnetic anisotropy in a direction perpendicular to the film surface, and the magnetic film holds the recording magnetic domain formed therein. The magneto-optical recording medium further comprises an intermediate layer and a reproducing aid layer between the reproducing layer and the recording layer. Saturated magnetization of the reproducing aid layer increases with an increase in the temperature of the reproducing aid layer. In a temperature range where reproduction is performed by irradiation of reproducing light, the recording magnetic domain of the recording layer is transcribed onto the reproducing layer via the reproducing aid layer, and the information recorded in the recording layer is reproduced. The reproducing layer is a vertical magnetic film having a magnetic characteristic such that outside the reproducing temperature range, the recording magnetic domain in the reproducing layer transcribed from the recording layer shrinks and disappears.
According to another aspect of the present invention, a magneto-optical recording medium includes a substrate; and a reproducing layer and a recording layer provided on the substrate. A recording magnetic domain is provided in the recording layer by heating the recording layer by irradiation with light and applying a recording magnetic field to the recording layer in such a manner that information is recorded in the recording layer. The recording layer is a magnetic film having magnetic anisotropy in a direction perpendicular to the film surface, and the magnetic film holds the recording magnetic domain formed therein. The magneto-optical recording medium further comprises an intermediate layer and a reproducing aid layer between the reproducing layer and the recording layer. In the reproducing aid layer, magnetic anisotropy in an in-plane direction parallel to the film surface is changed to magnetic anisotropy in a direction perpendicular to the film surface, as temperature of the reproducing aid layer is increased. In a temperature range where reproduction is performed by irradiation of reproducing light, the recording magnetic domain of the recording layer is transcribed onto the reproducing layer via the reproducing aid layer, and the information recorded in the recording layer is reproduced. The reproducing layer is a vertical magnetic film having a magnetic characteristic such that outside the reproducing temperature range, the recording magnetic domain in the reproducing layer transcribed from the recording layer shrinks and disappears.
In one embodiment of this invention, the reproducing aid layer is a magnetic film having a characteristic such that saturated magnetization is maximized when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the reproducing aid layer is a magnetic film having a characteristic such that the magnetic anisotropy in a direction perpendicular to the film surface is maximized when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the reproducing aid layer is a magnetic film having a characteristic such that the magnetic anisotropy in an in-plane direction parallel to the film surface is dominant at room temperature, and the magnetic anisotropy in a direction perpendicular to the film surface is dominant when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the reproducing aid layer is a magnetic film having a characteristic such that the magnetic anisotropy in an in-plane direction parallel to the film surface is dominant in a temperature range higher than when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the reproducing aid layer is a magnetic film having a characteristic such that film surface temperature of a portion of a light spot is greater than or equal to a Curie temperature when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the intermediate layer is made of a non-magnetic material.
In one embodiment of this invention, the non-magnetic intermediate layer is made of dielectric film or non-magnetic alloy film.
In one embodiment of this invention, the non-magnetic intermediate layer is made of a non-magnetic alloy reflecting film including at least one of Al, Cu, Ag, and Au.
In one embodiment of this invention, the non-magnetic intermediate layer is made of an oxide or nitride dielectric film including at least one of Si, Al, Ta, and Ge; a chalcogen-based compound dielectric film: or a mixed dielectric film including at least one of said dielectric films.
In one embodiment of this invention, the intermediate layer is made of magnetic material having magnetic anisotropy in an in-plane direction parallel to the film surface.
In one embodiment of this invention, the intermediate layer is a magnetic film having a characteristic such that film surface temperature of a portion of a light spot is greater than or equal to a Curie temperature when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, the reproducing layer is a magnetic film of a magnetic domain wall shrink type.
In one embodiment of this invention, the reproducing layer is a magnetic film of a magnetic domain wall shrink type; and the size of the recording magnetic domain provided in the recording layer is different from the size of the recording magnetic domain in the reproducing layer transcribed from the recording layer in the reproducing temperature range.
In one embodiment of this invention, the reproducing layer is a magnetic film of a magnetic domain wall shrink type; and the recording magnetic domain in the reproducing layer transcribed from the recording layer in the reproducing temperature range is stable only when the size thereof is greater than or equal to a predetermined size.
In one embodiment of this invention, the reproducing layer is a magnetic film of a magnetic domain wall shrink type; and the reproducing layer has a compensation composition temperature between room temperature and the Curie temperature.
In one embodiment of this invention, a magnetic domain wall is moved in the reproducing layer in a temperature region around the transcribing temperature when transcribing from the recording layer in the reproducing temperature range.
In one embodiment of this invention, the recording layer is a magnetic film having a characteristic such that saturated magnetization is maximized when reproducing the information magnetically transcribed from the recording layer.
In one embodiment of this invention, in a temperature region from room temperature Troom to transcribing temperature Tsw1, a force eliminating the recording magnetic domain in the reproducing layer is greater than a magnetic coupling force between the recording layer, and the reproducing layer and the reproducing aid layer; and in a temperature region greater than or equal to the transcribing temperature Tsw1, a magnetic coupling force from the recording layer is greater than the force eliminating the recording magnetic domain in the reproducing layer, so that the recording magnetic domain held in the recording layer is transcribed onto the reproducing layer via the reproducing aid layer.
In one embodiment of this invention, Troom less than Tsw1 less than Tc1 and Troom less than Tsw1 less than Tc3 are satisfied where Tc1 is the Curie temperature of the reproducing layer, Troom is room temperature, and Tsw1 is the transcribing temperature.
In one embodiment of this invention, the reproducing aid layer is a magnetic film such that the magnetic anisotropy in an in-plane direction parallel to the film surface is dominant in a temperature region less than the transcribing temperature Tsw1, and the magnetic anisotropy in a direction perpendicular to the film surface is dominant in a temperature region greater than or equal to the transcribing temperature Tsw1.
In one embodiment of this invention, the recording layer, the reproducing layer, and the reproducing aid layer are made of rare earth-transition metal amorphous alloy.
According to another aspect of the present invention, a method for reproducing information from a magneto-optical recording medium, wherein in a reproducing temperature range around a temperature at which saturated magnetization of a recording layer is maximized, a magnetic coupling force between the recording layer and a reproducing layer via a reproducing aid layer is greater than a force shrinking a magnetic domain wall of the reproducing layer, and a recording magnetic domain recorded in the recording layer is transcribed onto the reproducing layer so that the information is reproduced, includes the steps of: increasing the temperature of the magneto-optical recording medium irradiated by laser light and included in an inside part of a light spot to a temperature range including a temperature at which the saturated magnetization of at least the recording layer or the reproducing aid layer is maximized; and reproducing the information only from a temperature region within the light spot where the information can be transcribed from the recording layer by a magnetic coupling force between the recording layer and the reproducing layer, by transcribing the recording magnetic domain from the recording layer onto the reproducing layer.
In one embodiment of this invention, in the reproducing step, the size of the recording magnetic domain transcribed onto the reproducing layer is enlarged and the information is detected.
In one embodiment of this invention, in the reproducing step, the information is detected while applying an external magnetic field to the reproducing layer.
According to another aspect of the present invention, an apparatus for reproducing information from a magneto-optical recording medium, wherein in a reproducing temperature range around a temperature at which saturated magnetization of a recording layer is maximized, a magnetic coupling force between the recording layer and a reproducing layer via a reproducing aid layer is greater than a force shrinking a magnetic domain wall of the reproducing layer, and a recording magnetic domain recorded in the recording layer is transcribed onto the reproducing layer so that the information is reproduced, includes: a heating section for increasing the temperature of the magneto-optical recording medium irradiated by laser light and included in an inside part of a light spot to a temperature range including a temperature at which saturated magnetization of at least the recording layer or the reproducing aid layer is maximized. The information is detected only from a temperature region within the light spot where the information can be transcribed from the recording layer by a magnetic coupling force between the recording layer and the reproducing layer, by transcribing the recording magnetic domain from the recording layer onto the reproducing layer.
According to another aspect of the present invention, a magneto-optical recording medium, includes: a substrate; and a reproducing layer and a recording layer provided on the substrate. A recording magnetic domain is provided in the recording layer by heating the recording layer by irradiation with light and applying a recording magnetic field to the recording layer in such a manner that information is recorded in the recording layer; the recording layer is a magnetic film having magnetic anisotropy in a direction perpendicular to the film surface, and the magnetic film holds the recording magnetic domain formed therein; the magnetic domain recorded in the recording layer is transcribed onto the reproducing layer in a vertical magnetization direction; and a coercive force of the reproducing layer is smaller than a transcribing magnetic field from the recording layer to the reproducing layer in a temperature region greater than or equal to a reproducing and transcribing temperature at which the magnetic domain of the recording layer is transcribed onto the reproducing layer.
According to another aspect of the present invention, a magneto-optical recording medium, includes: a substrate; and a reproducing layer and a recording layer provided on the substrate. A recording magnetic domain is provided in the recording layer by heating the recording layer by irradiation with light and applying a recording magnetic field to the recording layer in such a manner that information is recorded in the recording layer; the recording layer is a magnetic film having magnetic anisotropy in a direction perpendicular to the film surface, and the magnetic film holds the recording magnetic domain formed therein; the magnetic domain recorded in the recording layer is transcribed onto the reproducing layer in a vertical magnetization direction; and a coercive force of the reproducing layer is smaller than the intensity of a magnetic field inverting magnetization of the recording layer in a temperature region greater than or equal to a reproducing and transcribing temperature at which the magnetic domain of the recording layer is transcribed onto the reproducing layer.
According to another aspect of this invention, a magneto-optical recording medium, includes: a substrate; and a reproducing layer and a recording layer provided on the substrate. A recording magnetic domain is provided in the recording layer by heating the recording layer by irradiation with light and applying a recording magnetic field to the recording layer in such a manner that information is recorded in the recording layer; the recording layer is a magnetic film having magnetic anisotropy in a direction perpendicular to the film surface, and the magnetic film holds the recording magnetic domain formed therein: the magnetic domain recorded in the recording layer is transcribed onto the reproducing layer in a vertical magnetization direction; and a coercive force of the reproducing layer is smaller than a force moving a magnetic domain wall of the reproducing layer in a temperature region greater than or equal to a reproducing and transcribing temperature at which the magnetic domain of the recording layer is transcribed onto the reproducing layer.
In one embodiment of this invention, the magneto-optical recording medium includes a disk substrate on which prepits are discretely provided; a recording layer in which information is recorded by a magnetization having a vertical direction; and a reproducing layer onto which a magnetic domain recorded in the recording layer is transcribed by the magnetization having a vertical direction.
In one embodiment of this invention, a guide groove has a convex-and-concave shape and is provided on the disk substrate.
In one embodiment of this invention, the reproducing layer, onto which a magnetic domain recorded in the recording layer is transcribed by the magnetization having a vertical direction, is magnetically separated between each information track.
In one embodiment of this invention, at least a magnetic layer having magnetic anisotropy in a direction perpendicular to the film surface is provided between the recording layer and the reproducing layer; a magnetic domain recorded in the recording layer is transcribed onto the reproducing layer by the magnetization having a vertical direction; and the Curie temperature of the at least magnetic layer is smaller than the Curie temperature of the recording layer and the reproducing layer.
In one embodiment of this invention, the reproducing layer, onto which a magnetic domain recorded in the recording layer is transcribed by the magnetization having a vertical direction, has a compensation composition temperature smaller than the reproducing and transcribing temperature at which the magnetic domain of the recording layer is transcribed onto the reproducing layer.
In one embodiment of this invention, the magneto-optical recording medium further includes a non-magnetic intermediate layer between the recording layer and the reproducing layer: and a magnetic domain recorded in the recording layer is transcribed onto the reproducing layer by the magnetization having a vertical direction.
In one embodiment of this invention, the magneto-optical recording medium further comprises an intermediate magnetic layer between the recording layer and the reproducing layer; a magnetic domain recorded in the recording layer is transcribed onto the reproducing layer by the magnetization having a vertical direction; and the intermediate magnetic layer has an in-plane magnetic anisotropy in a temperature region smaller than or equal to the reproducing and transcribing temperature at which the magnetic domain of the recording layer is transcribed onto the reproducing layer.
In one embodiment of this invention, a coercive force of the reproducing layer is smaller than the intensity of a modulated magnetic field when recording in a temperature range of from room temperature to about 100xc2x0 C.
In one embodiment of this invention, a coercive force of the recording layer is greater than or equal to about 3K Oe at room temperature; and the coercive force is smaller than or equal to about 500 Oe in a temperature range of from about 200xc2x0 C. to about 250xc2x0 C.
According to another aspect of the present invention, a method for reproducing recorded information from the magneto-optical recording medium is provided, wherein a light beam is moved relative to the medium; the medium is irradiated with the light beam from the reproducing layer side; a temperature distribution which has a gradient in a moving direction of a spot of the light beam is provided on the medium; the temperature distribution includes a temperature region greater than at least the Curie temperature of an intermediate magnetic layer; a magnetic domain wall of a transcribed magnetic domain of the reproducing layer is moved; and a change in polarized plane of a reflected light of the light beam is detected to reproduce the recorded information. The intermediate magnetic layer is provided between the reproducing layer and the recording layer.
According to another aspect of the present invention, an apparatus for reproducing recorded information from the magneto-optical recording medium is provided, wherein the apparatus comprises a heating section for providing a temperature distribution which has a gradient in a moving direction of a spot of a light beam on the magneto-optical recording medium; and a change in polarized plane of a reflected light of the light beam is detected to reproduce the recorded information.
According to this invention, the above-described structure allows minimization of the coercive force in the reproducing layer when the temperature thereof is increased. This weakens the force blocking and obstructing the magnetic domain wall in the recording domain, thereby securing a sufficient magnetic domain wall mobility even for high-density recording.
Further, the formation of discrete prepits in the substrate leads to a reduction in coercive force in the reproducing layer. A force based on the substrate shape which blocks the magnetic domain wall shift also can be reduced. The coercive force is reduced to about 500 Oe or less by a temperature of about 150xc2x0 C. or higher so that sufficient recording and reproducing characteristics are secured.
In a method using the magnetically induced super-resolution such as FAD and RAD, a reproducing field or initializing magnetic field is required upon reproduction of a signal. According to this invention, an external magnetic field is not required upon reproduction of a signal. The magnetization of the reproducing layer upon recording a signal is sufficiently small and does not exert an influence on the recording magnetic field characteristic.
Furthermore, in particular, there is substantially no influence from noise caused by the groove shape when both land and groove are used for recording for the purpose of high-density recording. SNR is therefore excellent. Signal characteristics are effectively improved when a track pitch is narrow.
Thus, the invention described herein makes possible the advantages of providing: (1) a magneto-optical recording medium having a high resolution and high performance without the use of an initializing magnetic field, in which in a particular temperature region within a reproducing light spot, two operating characteristics, i.e., a magnetic super-resolution mask due to a shrink operation (a magnetic domain wall shrink operation) or magnetic domain wall shift and a transcription capability of a reproducing layer for a recording signal, can both be improved; (2) a method for reproducing the above-described magneto-optical recording medium suitable for high-density recording; and (3) an apparatus for reproducing the above-described magneto-optical recording medium suitable for high-density recording.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.